The Divi Membership plugin for WordPress is vulnerable to Authentication Bypass in all versions up to, and including, 2.3.0. The processpaypalcallback function, hooked to the init action, accepts a base64-encoded paypalparam GET parameter with no IPN validation, no cryptographic signature check, no ownership verification, and no nonce, allowing it to trust an entirely attacker-controlled user ID value that is passed directly to wpsetcurrentuser() and wpsetauthcookie(). This makes it possible for unauthenticated attackers to log in as any existing WordPress user — including administrators — by supplying an arbitrary user ID in the paypalparam GET parameter, resulting in full site takeover. The vulnerability is further compounded by the fact that the PayPal gateway class is instantiated unconditionally regardless of whether PayPal is enabled or configured, ensuring the vulnerable hook is always registered on every front-end request.